Problem: In his physics class, William took 5 quizzes. His scores were 78, 89, 80, 86, and 97. What was his average score on the quizzes?
The average is the sum of his scores divided by the number of scores. There are 5 scores and their sum is $78 + 89 + 80 + 86 + 97 = 430$ His average score is $430 \div 5 = 86$.